Real time switching between worlds

Hello everyone, This is the first time i ask a question, I am working on project (third person) I have two characters(A, B)
And a door what i wont is if I enter this door it changes automatically from A to B and the same with object if a black cube enters the door, it turns red even if I don’t go through that door (similar to fortnite tilted town season X) and which method will work smoothly . (C ++ or Blueprint) im use 4.25.1

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